Method and apparatus for coding information, method and apparatus for decoding coded information, method of fabricating a recording medium, the recording medium and modulated signal

ABSTRACT

In the coding device and method, m-bit information words are converted into n-bit code words such that the coding rate m/n is greater than ⅔. The n-bit code words are divided into a first type and a second type, and into coding states of a first kind and a second kind such that an m-bit information word is converted into an n-bit code word of the first or second kind if the previous m-bit information word was converted into an n-bit code word of the first type and is converted into an n-bit code word of the first kind if the previous m-bit information word was converted into an n-bit code word of the second type. In one embodiment, n-bit code words of the first type end in zero, n-bit code words of the second type end in one, n-bit code words of the first kind start with zero, and n-bit code words of the second kind start with zero or one. Furthermore, in the embodiments, the n-bit code words satisfy a dk-constraint of (1,k) such that a minimum of 1 zero and a maximum of k zeros falls between consecutive ones. The coding device and method are employed to record information on a recording medium and thus create the recording medium. The coding device and method are further employed to transmit information. In the decoding method and apparatus, n-bit code words are decoded into m-bit information words. The decoding involves determining the state of a next n-bit code word, and based on the state determination, the current n-bit code word is converted into an m-bit information word. The decoding device and method are employed to reproduce information from a recording medium, and to receive information transmitted over a medium.

CROSS-REFERENCE TO RELATED APPLICATION

present application is a continuation of co-pending application Ser. No.10/902,920 filed on Aug. 2, 2004, which is a continuation of applicationSer. No. 09/707,947 filed on Nov. 8, 2000. The present application alsoclaims priority to EPO Patent Application No. 99203739.0, filed Nov. 11,1999, and application Ser. No. 09/707,947 the entire contents of bothwhich are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to coding information, and moreparticularly, to a method and apparatus for coding information havingimproved information density. The present invention further relates toproducing a modulated signal from the coded information, producing arecording medium from the coded information, and the recording mediumitself. The present invention still further relates to a method andapparatus for decoding coded information, and decoding coded informationfrom a modulated signal and/or a recording medium.

BACKGROUND OF THE INVENTION

When data is transmitted through a transmission line or recorded onto arecording medium such as a magnetic disc, an optical disc or amagneto-optical disc, the data is modulated into code matching thetransmission line or the recording medium prior to the transmission orrecording.

Run length limited codes, generically designated as (d,k) codes, havebeen widely and successfully applied in modern magnetic and opticalrecording systems. Such codes, and means for implementing such codes aredescribed by K. A. Schouhamer Immink in the book entitled “Codes forMass Data Storage Systems” (ISBN 90-74249-23-X, 1999). Run lengthlimited codes are extensions of earlier non return to zero recordingcodes, where binary recorded “zeros” are represented by no (magneticflux) change in the recording medium, while binary “ones” arerepresented by transitions from one direction of recorded flux to theopposite direction.

In a (d,k) code, the above recording rules are maintained with theadditional constraints that at least d “zeros” are recorded betweensuccessive “ones”, and no more than k “zeros” are recorded betweensuccessive “ones”. The first constraint arises to obviate intersymbolinterference occurring because of pulse crowding of the reproducedtransitions when a series of “ones” are contiguously recorded. Thesecond constraint arises to ensure recovering a clock from thereproduced data by “locking” a phase locked loop to the reproducedtransitions. If there is too long an unbroken string of contiguous“zeros” with no interspersed “ones”, the clock regeneratingphase-locked-loop will fall out of synchronism. In, for example, a (1,7)code there is at least one “zero” between recorded “ones”, and there areno more than seven recorded contiguous “zeros” between recorded “ones”.

The series of encoded bits is converted, via a modulo-2 integrationoperation, to a corresponding modulated signal formed by bit cellshaving a high or low signal value. A “one” bit is represented in themodulated signal by a change from a high to a low signal value or viceversa, and a “zero” bit is represented by the lack of change in themodulated signal.

The information conveying efficiency of such codes is typicallyexpressed as a rate, which is the quotient of the number of bits (m) inthe information word to the number of bits (n) in the code word (i.e.,m/n). The theoretical maximum rate of a code, given values of d and k,is called the Shannon capacity. FIG. 1 tabulates the Shannon capacityC(d,k) for d=1 versus k. As shown, for a (1,7) code, the Shannoncapacity, C(1,7), has a value of 0.67929. This means that a (1,7) codecannot have a rate larger than 0.67929. The practical implementation ofcodes requires that the rate be a rational fraction, and to date theabove (1,7) code has a rate ⅔. This rate of ⅔ is slightly less than theShannon capacity of 0.67929, and the code is therefore a highlyefficient one. To achieve the ⅔ rate, 2 unconstrained data bits aremapped into 3 constrained encoded bits.

(1,7) codes having a rate of ⅔ and means for implementing associatedencoders and decoders are known in the art. U.S. Pat. No. 4,413,251entitled “Method and Apparatus for Generating A Noiseless Sliding BlockCode for a (1,7) Channel with Rate ⅔”, issued in the names of Adler etal., discloses an encoder which is a finite-state machine having 5internal states. U.S. Pat. No. 4,488,142 entitled “Apparatus forEncoding Unconstrained Data onto a (1,7) Format with Rate ⅔”, issued inthe name of Franaszek discloses an encoder having 8 internal states.

However, a demand exists for even more efficient codes so that, forexample, the information density on a recording medium or over atransmission line can be increased.

SUMMARY OF THE INVENTION

In the converting method and apparatus according to the presentinvention, m-bit information words are converted into n-bit code wordsat a rate greater than ⅔. Consequently, the same amount of informationcan be recorded in less space, and information density increased.

In the present invention, n-bit code words are divided into a first typeand a second type, and into coding states of a first kind and a secondkind such that an m-bit information word is converted into an n-bit codeword of the first or second kind if the previous m-bit information wordwas converted into an n-bit code word of the first type and is convertedinto an n-bit code word of the first kind if the previous m-bitinformation word was converted into an n-bit code word of the secondtype. In one embodiment, n-bit code words of the first type end in zero,n-bit code words of the second type end in one, n-bit code words of thefirst kind start with zero, and n-bit code words of the second kindstart with zero or one. Furthermore, in the embodiments according to thepresent invention, the n-bit code words satisfy a dk-constraint of (1,k)such that a minimum of 1 zero and a maximum of k zeros falls betweenconsecutive ones.

In other embodiments of the present invention, the coding device andmethod according to the present invention are employed to recordinformation on a recording medium and create a recording mediumaccording to the present invention.

In still other embodiments of the present invention, the coding deviceand method according to the present invention are further employed totransmit information.

In the decoding method and apparatus according to the present invention,n-bit code words created according to the coding method and apparatusare decoded into m-bit information words. The decoding involvesdetermining the state of a next n-bit code word, and based on the statedetermination, the current n-bit code word is converted into an m-bitinformation word.

In other embodiments of the present invention, the decoding device andmethod according to the present invention are employed to reproduceinformation from a recording medium.

In still other embodiments of the present invention, the decoding deviceand method according to the present invention are employed to receiveinformation transmitted over a medium.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given herein below and the accompanying drawingswhich are given by way of illustration only, wherein like referencenumerals designate corresponding parts in the various drawings, andwherein:

FIG. 1 tabulates the Shannon capacity C(d,k) for d=1 versus k;

FIG. 2 shows an example of how the code words in the various subgroupsare allocated in to the various states in the first embodiment;

FIG. 3 shows an embodiment for a coding device according to theinvention;

FIGS. 4A-4H show a complete translation table according to the firstembodiment for converting 9-bit information words into 13-bit codewords;

FIG. 5 illustrates the conversion of a series of information words intoa series of code words using the translation table of FIGS. 4A-4H;

FIG. 6 illustrates an embodiment of a recording device according to thepresent invention;

FIG. 7 illustrates a recording medium and modulated signal according tothe present invention;

FIG. 8 illustrates a transmission device according to the presentinvention;

FIG. 9 illustrates a decoding device according to the present invention;

FIG. 10 illustrates a reproducing device according to the presentinvention;

FIG. 11 illustrates a receiving device according to the presentinvention;

FIG. 12 shows an example of how the code words in the various subgroupsare allocated in to the various states in the second embodiment;

FIGS. 13A-13C show the beginning, middle and end portions of atranslation table according to the second embodiment for converting9-bit information words into 13-bit code words;

FIG. 14 shows an example of how the code words in the various subgroupsare allocated in to the various states in the third embodiment;

FIGS. 15A-15C show the beginning, middle and end portions of atranslation table according to the third embodiment for converting11-bit information words into 16-bit code words

FIG. 16 shows an example of how the code words in the various subgroupsare allocated in to the various states in the fourth embodiment; and

FIGS. 17A-17C show the beginning, middle and end portions of atranslation table according to the fourth embodiment for converting13-bit information words into 19-bit code words.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The general coding method according to the present invention will bedescribed followed by a specific first embodiment of the coding method.Next, the general decoding method according to the present inventionwill be described in the context of the first embodiment. The variousapparatuses according to the present invention will then be described.Specifically, the coding device, recording device, transmission device,decoding device, reproducing device and receiving device according tothe present invention will be described. Afterwards, additional codingembodiments according to the present invention will be described.

Coding Method

According to the present invention, an m-bit information word isconverted into an n-bit code word such that the rate of m/n is greaterthan ⅔. The code words are divided into first and second types whereinthe first type includes code words ending with “0” and the second typeincludes code words ending with “1.” As a result, the code words of thefirst type are divided into two subgroups E00 and E10, and code words ofthe second type are divided into two subgroups E01 and E11. Code wordsubgroup E00 includes code words that start with “0” and end with “0”,code word subgroup E01 includes code words that start with “0” and endwith “1”, code word subgroup E10 includes code words that start with “1”and end with “0”, and code word subgroup E11 includes code words thatstart with “1” and end with “1”.

The code words are also divided into at least one state of a first kindand at least one state of a second kind. States of the first kindinclude code words that only start with “0,” and states of the secondkind include code words that start with either “0”or “1.”

Coding Method According to a First Embodiment

In a first preferred embodiment of the present invention, 9-bitinformation words are converted into 13-bit code words. The code wordssatisfy a (d,k) constraint of (1,k), and are divided into 3 states ofthe first kind and 2 states of the second kind (a total of 5 states). Inorder to reduce the k-constraint, three code words, namely,“0000000000000”, “0000000000001”, and “0000000000010” are barred fromthe encoding tables. An enumeration of code words shows there are 231code words in subgroup E00, 144 code words in subgroup E10, 143 codewords in subgroup E01, and 89 code words in subgroup E11.

To perform encoding, each 13-bit code word in each state is associatedwith a coding state direction. The state direction indicates the nextstate from which to select a code word in the encoding process. Thestate directions are assigned to code words such that code words thatend with a “0” (i.e. code words in subgroups E10 and E00) haveassociated state directions that indicate any of the r=5 states, whilecode words that end with a “1” (i.e., code words in subgroups E01 andE11) have associated state directions that only indicate one of thestates of the first kind. This ensures that the d=1 constraint will besatisfied; namely, after a code word ending in “1”, the next code wordwill start with “0”.

Furthermore, while, as explained in more detail below, the same codeword can be assigned to different information words in the same state,different states cannot include the same code word. In particular codewords in subgroups E10 and E00 can be assigned 5 times to differentinformation words within one state, while code words in subgroups E11and E01 can be assigned 3 times to different information words withinone state. As there are 231 code words in subgroup E00 and 144 codewords in subgroup E10, there are 1875 (5*(231+144)) “code word—statedirection” combinations for code words of the first type. There are 143code words in subgroup E01 and 89 code words in E11, so that there are696 (3*(143+89)) “code word—state direction” combinations for code wordsof the second type. In total 1875+696=2571 “code word—state direction”combinations exist.

For m-bit information words, there are a total of 2^(m) possibleinformation words. So, for 9-bit information words, 2⁹=512 informationwords exist. Because there are five states in this encoding embodiment,5 times 512=2561 of the “code word—state direction” combinations areneeded. This leaves 2571−2561=10 remaining combinations.

The available code words in the various subgroups are distributed overthe states of the first and second kind in compliance with therestrictions discussed above. FIG. 2 shows an example of how the codewords in the various subgroups are allocated in this embodiment to thevarious states. As shown in FIG. 2, in this example, states 1, 2, and 3are states of the first kind and states 4 and 5 are states of the secondkind. Taking the subgroup E00 of size 230 as an example, subgroup E00has 76 code words in each of states 1, 2, and 3 plus 1 code word in eachof states 4 and 5. And, taking state 1 as an example, in state 1 thenumber of “code word—state direction” combinations is 5×76+3×44=512,which means that 9-bit information words can be assigned. Remember, eachcode word of the first type can be assigned any one of the fivedifferent states as a state directions, and therefore used five timewithin a state; while each code word of the second type can only beassigned one of the three states of the first kind as a state directionbecause of the d=1 restriction, and therefore used three times within astate.

It can be verified that from any of the r=5 coding states shown in FIG.2 there at least 512 information words that can be assigned to codewords, which is enough to accommodate 9-bit information words. In themanner described above any random series of 9-bit information words canbe uniquely converted to a series of code words.

FIGS. 4A-4H show a complete translation table according to thisembodiment for converting 9-bit information words into 13-bit codewords. Included in the translation table of FIGS. 4A-4H are the statedirection assigned to each code word. Specifically, in FIGS. 4A-4H, thefirst column shows the decimal notation of the information words in thesecond column. The third, fifth, seventh, ninth and eleventh columnsshow the code words (also referred to in the art as channel bits)assigned to the information words in states 1, 2, 3, 4 and 5,respectively. The fourth, sixth, eighth, tenth and twelfth columns showby way of the respective digits 1, 2, 3, 4 and 5 the state direction ofthe associated code words in the third, fifth, seventh, ninth andeleventh columns, respectively.

The conversion of a series of information words into a series of codewords will be further explained with reference to FIG. 5. The firstcolumn of FIG. 5 shows from top to bottom a series of successive 9-bitinformation words, and the second column shows in parenthesis thedecimal values of these information words. The third column “state” isthe coding state that is to be used for the conversion of theinformation word. The “state” is laid down when the preceding code wordwas delivered (i.e., the state direction of the preceding code word).The fourth column “code words” includes the code words assigned to theinformation words according to the translation table of FIGS. 4A-H. Thefifth column “next state” is the state direction associated with thecode word in the fourth column and is also determined according to thetranslation table of FIGS. 4A-H.

The first word from the series of information words shown in the firstcolumn of FIG. 5 has a word value of “1” in decimal notation. Let usassume that the coding state is state 1 (S1) when the conversion of theseries of information words is initiated. Therefore the first word istranslated into code word “0000000000100” according to the state 1 setof code words from the translation table. At the same time the nextstate becomes state 2 (S2) because the state direction assigned to codeword “0000000000100” representing decimal value 1 in state 1 is state 2.This means that the next information word (decimal value “3”) is goingto be translated using the code words in state 2. Consequently, the nextinformation word, having a decimal value of “3”, is translated into codeword “0001010001010”. Similar to the manner described above, theinformation words having the decimal values “5”, “12” and “19” areconverted.

Decoding Method

Hereinafter, decoding of n-bit code words (in this example 13-bit words)received from a recording medium will be further explained withreference to FIGS. 4A-4H. For the purposes of description, assume thatthe word values of a series of successive code words received from, forexample, a recording medium are “0000000000100”, “0001010001010”,“0101001001001”. From the translation table of FIGS. 4A-4H, it is foundthat the first code word “0000000000100” is assigned to the informationwords “0”, “1”, “2”, “3” and “4” and state directions 1, 2, 3, 4 and 5,respectively. The next code word value is “0001010001010”, and belongsto the set of code words in state 2. This means that the first code word“0000000000100” had a state direction of 2. The first code word“0000000000100” with a state direction of 2 represents the informationword having a decimal value of “1”. Therefore, it is determined that thefirst code word represents information word “000000001” having a decimalvalue of “1”.

Furthermore, the third code word “0101001001001” is a member of state 4.Therefore, it is determined in the same manner as above that the secondcode word “0001010001010” represents the information word having thedecimal value “3”. In the same manner other code words can be decoded.It is noted that both the current code word and the next code words areobserved to decode the current code word into a unique information word.

Coding Device

FIG. 3 shows an embodiment for a coding device 124 according to theinvention. The coding device 124 converts m-bit information words inton-bit code words, where the number of different coding states r isrepresented by s bits. For example, when the number of coding statesr=5, s equals 3. As shown, the coding device 124 includes a converter 50for converting (m+s) binary input signals to (n+s) binary outputsignals. In a preferred embodiment, the converter 50 includes a readonly memory (ROM) storing a translation table according to at least oneembodiment of the present invention and address circuitry for addressingthe translation table based on the m+s binary input signals. However,instead of a ROM, the converter 50 can include a combinatorial logiccircuit producing the same results as the translation table according toat least one embodiment of the present invention.

From the inputs of the converter 50, m inputs are connected to a firstbus 51 for receiving m-bit information words. From the outputs of theconverter 50, n outputs are connected to a second bus 52 for deliveringn-bit code words. Furthermore, s inputs are connected to an s-bit thirdbus 53 for receiving a state word that indicates the instantaneouscoding state. The state word is delivered by a buffer memory 54including, for example, s flip-flops. The buffer memory 54 has s inputsconnected to a fourth bus 55 for receiving a state direction to beloaded into the buffer memory 54 as the state word. For delivering thestate directions to be loaded in the buffer memory 54, the s outputs ofthe converter 50 are used.

The second bus 52 is connected to the parallel inputs of aparallel-to-serial converter 56, which converts the code words receivedover the second bus 52 to a serial bit string. A signal line 57 suppliesthe serial bit string to a modulator circuit 58, which converts the bitstring into a modulated signal. The modulated signal is then deliveredover a line 60. The modulator circuit 58 is any well-known circuit forconverting binary data into a modulated signal such as a modula-2integrator.

For the purposes of synchronizing the operation of the coding device,the coding device includes a clock generating circuit (not shown) of acustomary type for generating clock signals for controlling timing of,for example, the parallel/serial converter 58 and the loading of thebuffer memory 54.

In operation, the converter 50 receives m-bit information words and ans-bit state word from the first bus 51 and the third bus 53,respectively. The s-bit state word indicates the state in thetranslation table to use in converting the m-bit information word.Accordingly, based on the value of the m-bit information word, the n-bitcode word is determined from the code words in the state identified bythe s-bit state word. Also, the state direction associated with then-bit code word is determined. The state direction, namely, the valuethereof is converted into an s-bit binary word; or alternatively, thestate directions are stored in the translation table as s-bit binarywords. The converter 50 outputs the n-bit code word on the second bus52, and outputs the s-bit state direction on fourth bus 55. The buffermemory 54 stores the s-bit state direction as a state word, and suppliesthe s-bit state word to the converter 50 over the third bus 53 insynchronization with the receipt of the next m-bit information word bythe converter 50. This synchronization is produced based on the clocksignals discussed above in any well-known manner.

The n-bit code words on the second bus 52 are converted to serial databy the parallel/serial converter 56, and then the serial data isconverted into a modulated signal by the modulator 58.

The modulated signal may then undergo further processing for recordationor transmission.

Recording Device

FIG. 6 shows a recording device for recording information that includesthe coding device 124 according to the present invention as shown inFIG. 3. As shown in FIG. 6, m-bit information is converted into amodulated signal through the coding device 124. The modulated signalproduced by the coding device 124 is delivered to a control circuit 123.The control circuit 123 may be any conventional control circuit forcontrolling an optical pick-up or laser diode 122 in response to themodulated signal applied to the control circuit 123 so that a pattern ofmarks corresponding to the modulated signal are recorded on therecording medium 110.

FIG. 7 shows by way of example, a recording medium 110 according to theinvention. The recording medium 110 shown is a read-only memory (ROM)type optical disc. However, the recording medium 110 of the presentinvention is not limited to a ROM type optical disk, but could be anytype of optical disk such as a write-once read-many (WORM) optical disk,random accessible memory (RAM) optical disk, etc. Further, the recordingmedium 110 is not limited to being an optical disk, but could be anytype of recording medium such as a magnetic disk, a magneto-opticaldisk, a memory card, magnetic tape, etc.

As shown in FIG. 7, the recording medium 110 according to one embodimentof the present invention includes information patterns arranged intracks 111. Specifically, FIG. 7 shows an enlarged view of a track 111along a direction 114 of the track 111. As shown, the track 111 includespit regions 112 and non-pit regions 113. Generally, the pit and non-pitregions 112 and 113 represent constant signal regions of the modulatedsignal 115 (zeros in the code words) and the transitions between pit andnon-pit regions represent logic state transitions in the modulatedsignal 115 (ones in the code words).

As discussed above, the recording medium 110 may be obtained by firstgenerating the modulated signal and then recording the modulated signalon the recording medium 110. Alternatively, if the recording medium isan optical disc, the recording medium 110 can also be obtained withwell-known mastering and replica techniques.

Transmission Device

FIG. 8 shows a transmission device for transmitting information thatincludes the coding device 124 according to the present invention asshown in FIG. 3. As shown in FIG. 8, m-bit information words areconverted into a modulated signal through the coding device 124. Atransmitter 150 then further processes the modulated signal, to convertthe modulated signal into a form for transmission depending on thecommunication system to which the transmitter belongs, and transmits theconverted modulated signal over a transmission medium such as air (orspace), optical fiber, cable, a conductor, etc.

Decoding Device

FIG. 9 illustrates a decoder according to the present invention. Thedecoder performs the reverse process of the converter of FIG. 3 andconverts n-bit code words of the present invention into m-bitinformation words. As shown, the decoder 100 includes a first look-uptable (LUT) 102 and a second LUT 104. The first and second LUTs 102 and104 store the translation table used to create the n-bit code wordsbeing decoded. Where K refers to time, the first LUT 102 receives the(K+1)th n-bit code word and the second LUT 104 receives the output ofthe first LUT 102 and the Kth n-bit code word. Accordingly, the decoder100 operates as a sliding block decoder. At every block time instant thedecoder 100 decodes one n-bit code word into one m-bit information wordand proceeds with the next n-bit code word in the serial data (alsoreferred to as the channel bit stream).

In operation, the first LUT 102 determines the state of the (K+1)th codeword from the stored translation table, and outputs the state to thesecond LUT 104. So the output of the first LUT 102 is a binary number inthe range of 1, 2, . . . , r (where r denotes the number of states inthe translation table). The second LUT 104 determines the possible m-bitinformation words associated with Kth code word from the Kth code wordusing the stored translation table, and then determines the specific oneof the possible m-bit information words being represented by the n-bitcode word using the state information from the first LUT 102 and thestored translation table.

For the purposes of further explanation only, assume the n-bit codewords are 13-bit code words produced using the translation table ofFIGS. 4A-4H. Then, referring to FIG. 5, if the (K+1)th 13-bit code wordis “0001010001010” the first LUT 102 determines the state as state 2.Furthermore, if the Kth 13-bit code word is “0000000000100”, then thesecond LUT 104 determines that the Kth 13-bit code word represents oneof the 9-bit information words having a decimal value of 0, 1, 2, 3 or4. And, because the next state or state direction of state 2 is suppliedby the first LUT 102, the second LUT 104 determines that the Kth 13-bitcode word represents the 9-bit information word having a decimal valueof 1 because the 13-bit code word “0000000000100” associated with astate direction of 2 represents the 9-bit information word having adecimal value of 1.

Reproducing Device

FIG. 10 illustrates a reproducing device that includes the decoder 100according to the present invention as shown in FIG. 9. As shown, thereading device includes an optical pick-up 122 of a conventional typefor reading a recording medium 110 according to the invention. Therecording medium 110 may be any type of recording medium such asdiscussed previously. The optical pick-up 122 produces an analog readsignal modulated according to the information pattern on the recordingmedium 110. A detection circuit 125 converts this read signal inconventional fashion into a binary signal of the form acceptable to thedecoder 100. The decoder 100 decodes the binary signal to obtain them-bit information words.

Receiving Device

FIG. 11 illustrates a receiving device that includes the decoder 100according to the present invention as shown in FIG. 9. As shown, thereceiving device includes a receiver 160 for receiving a signaltransmitted over a medium such as air (or space), optical fiber, cable,a conductor, etc. The receiver 160 converts the received signal into abinary signal of the form acceptable to the decoder 100. The decoder 100decodes the binary signal to obtain the m-bit information words.

Coding Method According to a Second Embodiment

FIGS. 12 and 13A-13C illustrate another embodiment of the presentinvention. According to this embodiment, the greater than ⅔ rate isachieved by converting 9-bit information words into 13-bit code words;wherein the number of coding states r equals 13, and 8 of the codingstates are coding states of the first kind and 5 of the coding statesare coding states of the second kind. Also, the code words satisfy a(d,k) constraint of (1,k). FIG. 12 corresponds to FIG. 2 of the firstembodiment, and illustrates the division of code words among the statesin this second embodiment.

As described above, code words that end with a “0”, i.e. code words insubgroups E00 and E10, are allowed to enter any of the r=13 states,while code words that end with a “1” i.e. code words in subgroups E01and E11, may only enter the states of the first kind (State 1 to State8).

Therefore, code words in subgroups E00 and E10 can be assigned 13 timesto different information words, while code words in subgroups E01 andE11 can be assigned 8 times to different information words. Referring toFIG. 12, subgroup E00 has 24 code words in state 1 and the subgroup E01has 25 code words in state 1. So the number of “code words—statedirection” combinations is (13×24)+(8×25)=512, which means that 9-bitinformation words can be assigned. It can be verified that from any ofthe r=13 coding states there at least 512 information words that can beassigned to code words, which is enough to accommodate 9-bit informationwords.

FIGS. 13A-13C illustrate the beginning, middle and end portions of thetranslation table for this second embodiment in the same fashion thatFIGS. 4A-4H illustrated the translation table for the first embodiment.

Coding Method According to a Third Embodiment

FIGS. 14 and 15A-15C illustrate another embodiment of the presentinvention. According to this embodiment, the greater than ⅔ rate isachieved by converting 11-bit information words into 16-bit code words;wherein the number of coding states r equals 13, and 8 of the codingstates are coding states of the first kind and 5 of the coding statesare coding states of the second kind. Also, the code words satisfy a(d,k) constraint of (1,k). FIG. 14 corresponds to FIG. 2 of the firstembodiment, and illustrates the division of code words among the statesin this third embodiment. It can be verified that from any of the r=13coding states there at least 2048 information words that can be assignedto code words, which is enough to accommodate 11-bit information words.

FIGS. 15A-15C illustrate the beginning, middle and end portions of thetranslation table for the third embodiment in the same fashion thatFIGS. 4A-4H illustrated the translation table for the first embodiment.

Coding Method According to a Fourth Embodiment CODING METHOD ACCORDINGTO A FOURTH EMBODIMENT

FIGS. 16 and 17A-17C illustrate another embodiment of the presentinvention. According to this embodiment, the greater than ⅔ rate isachieved by converting 13-bit information words into 19-bit code words;wherein the number of coding states r equals 5, and 3 of the codingstates are coding states of the first kind and 2 of the coding statesare coding states of the second kind. Also, the code words satisfy a(d,k) constraint of (1,k). FIG. 16 corresponds to FIG. 2 of the firstembodiment, and illustrates the division of code words among the statesin this fourth embodiment. It can be verified that from any of the r=5coding states there at least 8192 information words that can be assignedto code words, which is enough to accommodate 13-bit information words.

FIGS. 17A-17C illustrate the beginning, middle and end portions thetranslation table for the fourth embodiment in the same fashion thatFIGS. 4A-4H illustrated the translation table for the first embodiment.

The invention has been described in detail with particular reference topreferred embodiments thereof, but it will be understood that variationsand modifications can be effected within the spirit and scope of theinvention.

1. A method of converting, comprising: receiving m-bit informationwords, where m is an integer; converting the m-bit information wordsinto n-bit code words, where n is an integer greater than m, the n-bitcode words being divided into a first type and a second type and intocoding states of a first kind and a second kind such that an m-bitinformation word is converted into an n-bit code word of the first orsecond kind if the previous m-bit information word was converted into ann-bit code word of the first type and is converted into an n-bit codeword of the first kind if the previous m-bit information word wasconverted into an n-bit code word of the second type.